Process for color cinematography on lenticular films



L. BASSAN PROCESS FOR COLOR CINEMATOGRAPHY Oct. 19, 1948. :-:r AL

ON LENTICULAR FILMS Filed May 10, 1945 Patented Oct. 19, 1948 PROCESS Fon COLOR OINEMATOGRAP ON lLEN'rIoULAn FILMS f' Laurent Bassani and Gaston Gagnepain,

t France Application May 10, 1945,. Serial No. 592,956 In France December 22, 1944 Paris The attempts made heretofore in order to print copies by contact on positive lenticular lrns from lenticular negative iilms have vnot proved satisfactory. This is due to the material impossibility of accurately registering the minute lenticulations of both films, so that the chromo-selected image corresponding to a lenticulation of the negative (that is the image of the coloured filter used for in the camera and given by this particular lenticulation) should be printed on .the

positive lm exactly in the same relative position with respect to the lenticulation of the positive nlm. Even if it were possible to provide for the most perfect registration for two correspondent lenticulations of the negative and positive films, and if vthe pitch and proiile of the lenticulation were absolutely identical for both films at the moment of their manufacture, the difference between the two films in tension, chemical composition, hygrometric conditions, etc., will be sumcient to bring about diierences in pitches at the time of printing copies and therefore shift the chromo-selected image of the positive out of their correct position with respect to the lenticulations thereof, thus destroying the quality of the projected coloured image.

An attempt to obviate this defect would consist in correcting this defect due to the discordance e of the image of the filter used in the camera with respect to the lenticulations of the positive by shifting the coloured lter used at the projection by a distance t proportional to e but of contrary direction. But as the amount of deviation e varies all along the positive film, )t would have to be constantly modified.

NOW, applicants found that it is possible to attenuate to a certain extent the defects of the printed copy by giving to the iilter used at the projection an oscillatory movement, the amplitude ko of which represents the average displacement which should be given to the projection filter in order to compensate for the average deviation of the elementary images with reference to the lentlcuations of the positive, the oscillation period being equal to the time an image iieldl of the film remains stationary behind the projection window.

It will be appreciated that, among the various positions that the projection filter will occupy in the course of an oscillation period, at least one will correspond with thev correct position, compensating for the deviations. Generally,

the iilter will have to pass through this position twice (once in going and once in returning) and the result obtained will be intermediate between 3 Claims. (Cl. 13B-16.4)

the optimum one and the worst one (no compensating offsetting of the projection filter for a deviation e of the positive images).

In practice, for reasons of symmetry or uniformity of the images projected on the screen, the oscillatory movement should not be a reciproeating rectilinear movement, but a movement of circular translation. This condition is essential when the lenticulations of the film form a cross-l lzatchlng respectively parallel and perpendicular to the axis of the iilm and when the 'filter itself forms a crosshatching of diierently coloured zones.

The result can be considerably improved by imparting to the lter of the camera, at the View taking, a movement of circular translation with an amplitude producinga circular translation of the elementary images of the negative around their medium position with an amplitude distinctly larger than they average deviation so. but of course smaller than such a one that would provoke an entire substitution of the image of a iilter element for the image of another filter element, and by imparting to the projection filter an identical circular translation movement (taking in consideration the scale of the projection with respect to the scale of the view taking in the camera).

In this manner, the deviations e of the positive images from their accurate positions, which lead to the imperfections of the copy, are small in comparison with the systematical deviations brought about by the circular translation of the camera filter, whereby the effect of these devia,- tions e practically disappears at the restitution produced by the circular translation of the filter used at the projection, and the result becomes comparable to what could be Obtained with a lenticular negative film transformed into a posi"- tive one by a photographic treatment of inversion.

Another advantage of the circular translation of the camera lter is that the Whole eld of a lenticulation is swept by the image of the camera lter, so that the whole of said eld participates in the chromatic selection, whereas, in the ordinary method of taking views on lenticular iilms, the marginal parts of said eld do not receive any light and form on the positive opaque zones, which reduce the optical efficiency of the projection.

It will be noted that the circular translation of the camera filter causes between the adjacent areas of elementary chromatic selection which give an exact reproduction O- the coloured elements of the filter, intermediate areas where the annees selection is not rigorous, as they have been successively swept by light rays which have passed through differently coloured elements of the lter. But, during the projection, the circular translation of the projection filter produces an actual exploration of the positive film, which, because of the identic movements of both filters (except for the scales of the amplitudes), compensates for the eect of the circular translation of the camera iilter and restores a correct projected image.

In practice, the best result will be usually obtained experimentally by regulating the amplitude and the phase of the translation of the projection lter, until the resultappearing on the projection screen will be the best. f

The invention also covers the apparatus for carrying out the above mentioned process and the lms obtained thereby.

The mechanism for imparting to the filters the circular translation movement is preferably constituted as described in United States Patent No. 1,575,408.

Further characteristics of the invention will be apparent from the following description, with reference to the annexed drawing which shows, by way of example, an embodiment of the invention and in which:

Fig. 1 is a diagrammatical view illustrating the exposure of a lenticular film;

Fig. 2 shows, on a smaller scale, a lter to be used in the camera and the projector;

Fig. 3 diagrammatically illustrates the operation of printing on a positive film by contact;

Fig. 4 shows the effect of the deviation of the image of the lter given by a lenticular element, and

Fig. 5 diagrammatically shows a control device Without the lenticulations, lens 2 would give an image a from point A of the subject, an image o from point O and an image c from point C. But each lenticulation of the lm produces on the emulsion an image of filter 3, so that the image a of point A is constituted in fact by a chromo-selection G'A-B'A--R'A corresponding to the zones R-B-G of i'lter 3. In the same.

way, the image o is constituted by a chromoseleetion G'O--BO-RO and the image c by a chromo-selection G'C-B'CRC. For the projection, the lens of the projector must be associated with a lter similar to camera ilter 3 and it will be understood that, if the relation of lter 3 with respect to lm i is the same at the projecti-on as at the taking of the view, the lenticulations of the lm I and the lens of the projector will cooperate togrestitute the coloured image of the subject, as is well known in the art.

However, in orderto obtain this result, it is obviously necessary that the chromo-selection of each lenticulation of the projected positive lm (that is the image C'A-B'A-R'A of lter 3, given by the corresponding lenticulation) shall have a rigorously identic position asthe negative chromo-selection relatively to the corresponding lenticulation of the negative lm.

'Ihis result is necessarily obtained when the e the positive lm is produced from a negative iilm by contact printing (Fig. 3), the above mentioned condition cannot be practically fulfilled.

Contact printing, as shown in Fig, 3, is obtained by positioning the developed negative film N in contact with the unexposed positive film P, the emulsion coatings being in contact, and in order that the chromo-selection S should occupy in the positive lm P the same relative position with respect to the lenticulation LP, as the chromo-selection in the negative ilm with respect to the lenticulation LN, it is necessary that:

1. All the lenticulations IN and LP should be exactly identical and have the same pitch;

2. The optical axis of each lenticulation LP should exactly coincide with the optical axis of the opposite lenticulation IN.

As above explained, even admitting that the registering of the two films should be possible in a perfect form for a pair of corresponding positive and negative lenticulations, i. e. that the optical axes of both these lenticulations could be brought into 'perfect coincidence along X-X, the differences in tension between the two lms, the variations in their chemical composition, hygrometric condition, will be such that the same condition will not be fulfilled for the other p airs Y of lenticulations LN-LP.

Fig. 4 shows the eiect of a deviation e between the actual position of the image G'BR of illter GBR relatively to the positive lenticulation LP and the image G"B"R" which would have been obtained, had the positive film been produced by inversion of the negative, instead of being produced by contact printing.

The parts G B"' R" of the image on the correct film are intended to project respectively green, blue and red images on the screeny and at the projection they respectively cover the green, blue and red lters. If a defective copy is used, the images G', B', R' which are for instance -shifted downwardly with respect to images G" B" R will be substituted therefor. Considering for instance the image B', it will be seen on the drawing that the beam of white light f which passes through the lower part of image G' and should normally project a green color will pass through the blue filter and will therefore project a blue color. of white light f which passes through the lower part of image B' and should normally project a blue color will pass through the red filter and will thus' project a red color on the screen. 'I'he whole image on the screen, corresponding to the lenticulation considered will thus be formed partly in correct colors and partly in wrong colors, so that the whole projection will be defective so far as a true color reproduction is concerned.

It will be understood that, in order to establish. the correct conditions of the restitution of the exact image, it would be sumcient to' displace the projection screen 3 with respect to the theoretical position shown in the drawing, by a distance A proportional to e, but of reverse direction. However, as already explained, the deviation e varies all along the posiitve lm, so that the correction 7( cannot be constant during the whole time of a projection.

As previously mentioned, the invention consists in giving to the projection lter 3' an oscillatory movement, whose amplitude M represents the average offset or displacement to be given to the projection lter in order to compensate for the deviation eo of the elementary images G'B'R' with respect to the positive lenticulation LP, the

Similarly, the beam'A oscillation peiod being equal to the time an image ileld remains behind the projection window.

.As a rule, and more specifically when the illters 3l 3' are crosshatched as shown on Flg.12, the oscillation movementv to be imparted to the projection filter will be a circular translation, which can for instance be achieved by a mechanism such as that, shown dlagrammatically on Fig. 5, where illter 3 has two lugs 5 pivote'd about a pivot pin 6, supported by a nut 1, guided in a slide 8, carried by a helical gear, the centre of which is shown at m. Nut 'l is engaged by a micrometric screw I0, the head of which is milled and provided' with a, graduated scale cooperating with an index I2. The helical gear 9 meshes for instance with a worm I3 keyed upon a shaft I4, controlled by a pinion I5 actuated at a constant speed by any suitable motor. On shaft Il is keyed a second worm gear I3' in mesh with a helical gear 9 on which is mounted a device similar to the preceding one. It will be seen that, by turningthe knobs II, Il' by equal angles, relatively to index I2, I2', the eccentricity of the axes 6, 6', can be varied at will with respect to the centers n, n' oi plnions 9, 9. The rotation of shaft I4 thus produces a circular translation movement of screen 3', each point of which, such as M, describing a circle R whose radius is lio.

As above explained, the result can still be highly improved by imparting to the camera lter 3 a circular translation movement with an amplitude 8, producing a circular translation of the elementary images of the negative GBR' around their medium position, with an amplitude distinctly larger than the average deviation e0, but

smaller than the amplitude which would bring about a complete substiution of the image of a illter element for the image of another lter element for instance the complete substitution of the limage B' for the image C.

This circular translation of the camera screen 3 must be associated with a circular translation of the projection screen 3', the amplitude of these circular translations must be identical for both screens taking into account the scales of the images in the camera and on the 4projection screen. For carrying out this process,l the camera screen 3 and the projection screen 3 will be controlled by a mechanism of the type shown in Fig. 5, or still better by a pantograph mechanism such as described in the prior speciiication above referred to.

The circular translation of the camera illter affords a further advantage: as shown in Fig. l, the marginal sections T of each image field of a lenticulation vLN do not receive any light and therefore produce on the positive opaque areas which reduce the optical efilciency of the projection. `In the process according to this invention, the circular translation of lter 3 produces a sweeping of the whole image'eld corresponding to each lenticulation LN, which considerably reduces or eliminates the importance of the zones T which do not receive any light at the time when the view is taken. Y

As above explained, the partial overlap ot the images such as G'BR, as a result of such sweeping of each elementary ileld by the corresponding image ofthe iilter, produces between the areas of elementary chromatic selection such as G'- B-R. intermediate areas where the selection is not quite true, since they are successively swept by luminous rays which passed through diilerently coloured elements of illter 3. However, the circular translation of projection iilter 3' causes an exploration of the positive illm P which, due to the identity of the movements oi.' both nlters 3, 3 reduced to the proper scale `restitutes the correct projected image.

`sult`, the operator will. during the projection,

turn knobs II, II until the effect obtained on the projection screen will be satisfactory.

Obviously, the inventionv is not limited to the above described embodiment, which is given solely by way of example.

Having now described our invention what we claim as new and desire to secure by Letters Patent is:

1. A method of color cinematography which comprises projecting on a screen through an objective and a color filter elementary color selective images which have been formed on a lenticular lm and are adapted to occupy on said film variable positions from one particular i'llm to the other with respect to the corresponding lenticulation, the light, beam passing directly from the lenticular iilmto the color filter,'and imparting to the lter an oscillatory movement whose amplitude lis less than the amplitude corresponding to a displacement of an image on the lenticular lm equal to the smallestl cross-dimension of a lenticulation and proportional to the average displacement of the elementary images with respect to the corresponding lenticulation.

2. A method as claimed in claim 1, in which the said oscillatory movemet is a movement of circular translation.

3. A method according to claim l, in which the said elementary color selective images have been formed on the film by printing from a negative lenticular nlm.

LAURENT BASSANI.

GASTON GAGNEPAIN.

REFERENCES CITED The following references are of record in the Ille of this patent:

UNITED STATES PATENTS 

